Local-distant switch for superheterodyne receivers



sepi. 1, 1931. H. c. ALLEN LOCAL-019mm SWITCH-FOR SUPERHETERODYNE RECEIVERS Filed 001:. 7, 1930 Inventor: Horace QAllen, b5 Wm H is Attornea.

Patented Sept. 1, 1931 UNITED STATES Y-PATENT OFFICEF HORACE C. ALLEN, OI MERCHANTVILLE, NEW JERSEY, ASSIGNOR TO.GENERAL ELEC :TRIC COMPANY, CORPORATION OF NEW YORK LOCAL-DISTANT SWITCH FOR SUPERHETERODYN E RECEIVERS Application filed October 7, 1930. Serial No. 437,049.

The presentinvention relates to superheterodyne receiving apparatus and the like and more particularly it relates to a local-distant switch for receiving apparatus'of that char acter. r Y

The problem of protecting areceiving circuit from excessive voltages generated ma receiving antenna by 'local or high power transmitting stations may be met by providing a switch in the antenna circuit for disconnecting the antenna when receiving such stations. In connection with a sensitive superheterodyne receiving apparatus, this simple protective arrangement has been found to be not entirely satisfactory or effective, and it is the object of the present invention to provide an improved local-distant switch and circuit therefor which is particularly adapted to protect a superheterodyne receiving circuit from excessive voltages generated in the receiving antenna and to permit such apparatus to function properly when operating to receive any high power or'local station without signal distortion. i

The invention will be better understood from the following description when taken in connection with the accompanylng drawings and its scope will be pointed out in the ap-' pended claims. 1

In the drawmgsQFig. 1 is a'schematicwiring diagram of a portion of a switch embodying the invention, and Figs. 2 and 3 are modifications of the local-distant switch of Fig. 1.

Referring to Fig. 1, 5 is the first detector of a superheterodyne.receiver provided with" an input'circuit 6 connected to a source of radio frequency'signals 7 through a tuned input transformer 8. The detector is pro- 1 vided with an output or anode circuit 9 wh1ch superhetero- 'dyne receiver. provided with a local-distant the primary 10 of the transformer 11 is a' local-distant switch 14 which may be moved to a position'15 to provide adirect connection with'the transformer primary 10 through a compensating condenser 16, and which may be moved to an alternate position 17 to provide a connection with a tap point or tap18 on a resistor 19-20 which is connectedinl shunt with the output circuit.

The condenser 16, which is connected be-' tween the resistor 19-20 and the transformer 11, is a compensating device in connection with the output circuit for limiting the load provided by resistor 1920 on the primary of transformer 11. The condenser 16 prevents the load provided by the resistor from materiallyafi'ecting the frequency re-,

'spons'erange or characteristic of the'trans--' former 11, which in a 'superheterodyne receiver i's'set for a certain predetermined intermedlate frequency for use 1n connection with an'intermediate frequency amplifier; 1

The resistor 19 -20 is provided with thetap 18 at a pointsuch that the ratio between the resistance values of section 20 and of the whole resistor 19-20 is'in the same relation as the sensitivity ratios desired'for local and distant receptionj In the present'e'xample,

resistor section 20 may be substantially 2000 ohms, while resistor section 19 may be sub stantially 40000 ohms,' and the compensating device or condenser 16 may have a value of' substantially micromicrofarads.

It'will be seen thatwhen the local-distant "switch 14 is moved to the local positioi117,

the resistor'section 20 is connected in shunt with theoutput circuit while the resistor section 19 and the compensating condenser, 16 are connected in series with the output circuit and with the primary 10 of transformer 11. Resistor section 19 is therefore in circuit'with the primary 10 for limiting the transfer of energy to the transformer. When the local-distant switch is moved to the distant position 15 it will be seen that the output circuit is connected directly with the transformer primary 10 through the compensating device 16 while the load resistance at 1920 is connectedin shunt with the output' circuit. It has been found that by placing the local-distant control switch in the position indicated, between the first detector and the input transformer or coupling device for the intermediate frequency amplifier, an effective control of the signal strength applied to the receiver is obtained under wide-- affect the load placed upon the primary of the transformer or coupling device 11, whereby its frequencycharacteristic is not apprecirv bly changed by the. switching operations.

.Referringnow to Figs. 2 and 3. thelocah distant switching meansi provided in Fig, l hetween lines 21 and 22, are shown with slight modifications. .In 2, an additional circuit compensat-ing device or condenser is indicated at 23. This condenser is connected iii-the output circuit in such a manner that itxis short circuited by: the local-distant switch l iwhen thelatter is moved to its distant'po sition 15. and is included in circuit when the local-distant switch is moved to its local position 17. I

Thelfunction ot the compensating device 23 =isto provide in connection with the primary 10 of the transformer 11, a capacity load which compensates for the loss of the detector capacity load. In the presentexam plethe capacity of condenser 23 may be substantially 16 micromicrofarads. l vhenqthe local-distant switch l lis moved toits local position l7; the compensatingcondenser 23 is interposedin circuit between the load resistor19+20 and the detector. I V

; In Fig. 3,thecircuit is the same as in Fig. 2-except that theresistor section 19 omitted along withithecompensating condenser or device 16. This arrangement provides for a direct connection between the detector and the p-rimary of transformer 11 when the local-distant switch is moved to its distant position, and maintains the compensating con denser-23 in circuit when the-local-ditant switch is moved to the local position. In a circuit of this character, the resistance sec-- tion-:2O may be reduced to a value less than 2000 ohms or maybe increased -toa value as high'as 8000 ohms.

Its'willi benoted that in the modification shown in this figure, as well as the preceding tionwith adetector of the type indicated in the: present example.

lt is pointed out thatthe relative values R51 oi-the resistor sections 1920, in connection by Letters Patent of the United States, is:

In a superheteroi'lyne receiving appa= ratus, the combination of a signal detector having anoutput .circuit,.an amplifier coupling device connected with said output circuit, said coupling device having a predetermined frequency response characteristic switching means connected between said output circuit and the coupling device for chang-- ing the energy transfer from said output circuit to said device, and means arranged to be connected in circuit with said coupling device and said output circuit by said switchin means for- Jreventin a chan ein the frc- C t) D quency response characterstic of: said coupling device when operated.

2- In 'superheterodyne receiving "apparatusg the combination of asignal detector having an outputcircuit,; an amplifier-coin pling deviceconnected with said output circuit, said coupling device'having a predetermined frequency characteristic, .a resistor, a switch for connectino said resistor in circuit with said :coupling device andsaid detector for changingthe output of theilatter, and a condeuserlin circuit withsaid coupling device and resistor torniaintain-ing the load on said coupling;device; substantially constant.

3; In a radio receiving apparatus; the combination with a signal detector having an output circuit; of acoupling device having a predetermined frequency response range connected' with said output circuit to receive signal energy therefrom, SWltClllllglllQilllS 1nterposed in said output circuit for changing the load thereon and compensatingmcans connected in said output-circuit for-preventing said lead changes from affecting the fre-' quency response of said coupling device.

h Ina radioreceivingappa alas. the combination with a signal detector having an outputcircuit, of a transformer having a predetermined frequency response range connecteduvith said :output circuit to receive signal energy therefrom, a resistor, a con denser, circuit connections for said re vtor and condenserwith said output circuit and the" transformer, and switching Imeans arrangedto changc'said circuit connections of said resistor to limit the transferotcnergy froinsaid output circultto said transformer and with said condenser to preventa change of the frequency responserange of said trans l former when the ClICLilt'l connections are changed.

5; 111a superheterodyne radlo receiving apsaid switching means is paratus, a detector having an output circuit,

an input transformer for an intermediate fre-' quency amplifier connected with said output circuit, a resistor connected in shunt to said output circuit, said resistor being provided with a tap, a condenserconnected in said output circuit between the resistor and the transformer, a second condenser connected in the output circuit between the resistor and the detector, and a switching means connected with said output circuit resistor and last named condenser which is movable to one position to short circuit said condenser and to another position to remove said short circuit and to connect the detector output circuit to said tap on the resistor.

6. In a superheterodyne radio receiving apparatus, a detector having an output circuit, an input transformer for an intermediate frequency amplifier connected with said output circuit, a resistor, a condenser, and switching means for said out-put circuit connected with said resistor and said condenser and arranged to connect said resistor in shunt to said output circuit and said condenser in series therewith between said resistor and said input transformer.-

7. In a superheterodyne radio receiving apparatus, a detector having an output circuit, an input transformer for an intermediate frequency amplifier connected with said output circuit, a' resistor connected in shunt to said output circuit, said resistor being provided with a tap, a condenser connected in said out-put circuit between the resistor and the transformer, said condenser being proportioned to adjust the load on said transformer to a desired value, a second condenser connected in the output circuit between the resistor and the detector, said condenser having a value such that it'compensates for the detector capacity load on the transformer, and a switching means connected with said output circuit resistor and last named condenser which is movable to one position to short circuit said condenser and to another position to remove said short circuit and to connect the detector output circuit to said tap on the resistor.

8. In a superheterodyne receiver, the combination with a detector and a coupling device arranged to receive the signal output therefrom, said device having a certain frequency response characteristic of a local-distant switch means interposed between said detector and said transformer for changing the signal energy transferred to said transformer, said means including a resistor connected with the output circuit, switching means for changing the connection of said resistor to effect a change of the load on said output circuit, and I circuit compensating means in said output circuit for preventing a corresponding change in the load on said transformer, whereby the response character- 

